Let's walk through what's actually happening in your bowl. There are three usual suspects, and most of the time it's more than one.

Stale powder. Matcha is ground green tea leaves, and oxygen is the enemy. Once you pop the seal, oxidation starts. The volatile compounds that give fresh matcha its vivid color and sweet aroma also help stabilize the foam. After a few weeks, especially if the tin lives near the stove or in direct sunlight, the froth is the first thing to go. You might not taste a huge difference yet, but the texture tells the truth.

Water temperature. Boiling water is a froth killer. It denatures the proteins in the matcha that help trap air, leaving you with a bitter, flat brew. If you're just using a regular kettle and pouring straight from a rolling boil, you're sabotaging the froth before the whisk even touches it.

Whisk technique. Circles don't create foam; they just stir. Real froth needs air incorporated quickly, which means a back-and-forth motion that pulls bubbles into the liquid. A bamboo chasen with 80+ tines is designed for this, but even the right tool won't work if you're swirling it like a spoon.

One more trigger worth noting: weekend-only brewing means you might not remember the details from last week. You're more likely to skip sifting, use hotter water, or rush the whisking because you're doing it for the first time in days. It's not that you're a bad matcha maker—you're just out of practice.